diagnostics: rename diagnostic_output_file to diagnostics::output_file

diagnostics: rename diagnostic_output_file to diagnostics::output_file

No functional change intended.

gcc/ChangeLog:
	* diagnostic-format-html.cc: Update #include for move of
	diagnostic-output-file.h to diagnostics/output-file.h.  Update for
	move of diagnostic_output_file to diagnostics::output_file.
	* diagnostic-format-html.h: Likewise.
	* diagnostic-format-sarif.cc: Likewise.
	* diagnostic-format-sarif.h: Likewise.
	* diagnostic-output-spec.cc: Likewise.
	* diagnostic-output-spec.h (along): Likewise.
	* diagnostic-output-file.h: Move to...
	* diagnostics/output-file.h: ...here, updating header guard.
	(class diagnostic_output_file): Move to...
	(class diagnostics::output_file): ...here.
	* libgdiagnostics.cc (sarif_sink::sarif_sink): Update for
	move of diagnostic_output_file to diagnostics::output_file.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>